The mechanisms of a vertebrate motor pattern are being studied using the tongue neuromuscular system in the common boa, Constrictor constrictor, as a model system. Work to the present has described the tongue's movement patterns, the hypoglossal neurons, and the relation of these neurons to the tongue muscles. The proposed study will emphasize two aspects of fiber systems which are afferent to the boa hypoglossal nucleus. First, anatomical and physiological studies on cat motoneurons indicate that afferent terminals are morphologically distinguishable and are distributed differently on montoneurons of different sizes. Thus, the nature of synaptic boutons, upon each part of hypoglossal neurons will be studied by electron microscopy. Differences between neurons of different sizes will be emphasized. Second, movements of the cranial muscles, including the tongue, can be elicited by electrical stimulation of the forebrain in the boa. Thus the forebrain efferent tracts which subserve these movements will be studied using the Nauta and the Fink- Heimer techniques following lesions of the dorsal cortex, the dorsal striatum, and the ventral striatum.